Faulconer had previously backed the developer's efforts to bring a Major League Soccer expansion franchise to San Diego as a key component of the project, but hadn't officially endorsed the plan until now.

Their support came three days after San Diego State University, which has long eyed the land for campus expansion, broke off negotiations regarding the project. The developers led by La Jolla-based FS Investors had hoped the school would jointly pay for and use a joint soccer and college football stadium, and left the door open Thursday for the school to climb back on board.

The mayor said the proposal "checks all the boxes'' for the city's goals for the property, which was made available by the Chargers' decision to move to Los Angeles.

Along with the stadium, the project would result in a 60-acre park by the San Diego River, along with housing, offices and commercial space.

"I support this plan so we can leave something better for our kids,'' Faulconer said. "I support this plan as an Aztec alum, who can't wait for SDSU football to finally have the world-class home that it deserves. I think, most importantly, I support this plan as a San Diegan, who sees this rare opportunity for our city and wants to seize it.''

If the city doesn't move on the project now, the land will remain unused for years, he said. The mayor said he believes SoccerCity will transform Mission Valley the way Petco Park did for downtown and the East Village.

The developers sent a letter to the mayor on Thursday that capsulated a series of offers that would be included in a lease agreement -- including how to determine the purchase price, additional park acreage, community meetings, indemnification and inducements to SDSU, among other things.

San Diego State University issued a statement saying the university "shares the excitement of a joint-use stadium, affordable housing and a River Park, as well as the prospect of an MLS team here in San Diego. The FS Investors' initiative, however, is not in the best interests of the city of San Diego or of San Diego State University.''

"Good public policy for the redevelopment of this site demands the intelligent interest of all willing stakeholders, including the Mission Valley Planning Group, higher education, the environmental community, willing developers and the city of San Diego -- not a chosen few,'' the statement said.

Steve Altman, a member of the development group and longtime SDSU booster, said he was disappointed in the school's stance.

"Despite numerous efforts on my part, I failed to convince them months ago to come to the table and discuss their issues with us, many of which we feel are based on wrong assumptions on their part,'' Altman said.

"I join this group proud of the fact that we provide what I believe is a great solution to a real and immediate problem that is being faced by the university's football program, and I feel even stronger today about what we have done to accommodate San Diego State's needs,'' Altman said. "I hope that as time goes on, they will get behind this and support it because I think it is a very positive outcome for them.''

The developers collected more than 100,000 petition signatures in support of the project, and if enough are found to be valid, the City Council will have to decide whether to approve the plan or place it before voters -- likely in a special election in November.

The signatures are being verified by the Registrar of Voters office. County Registrar Michael Vu told City News Service that results will be forwarded to the city clerk on Wednesday.